Separating agent for optical isomers and process for producing the same

ABSTRACT

Polysaccharide derivative molecules are crosslinked exclusively among themselves on a support such as silica gel with the use of a polyfunctional crosslinking agent to immobilize the polysaccharide derivative on the support. The separating agent for optical isomers produced by the method has a high solvent resistance and, therefore, is most suitable as a separating agent for optical resolution.

FIELD OF THE INVENTION

The present invention relates to a separating agent for optical isomersand a process for producing the same. More particularly, it relates to aseparating agent, which is obtained by crosslinking polysaccharidederivative molecules only among themselves on a support and useful as anoptical resolution reagent for racemic modifications, and a process forproducing the same.

DESCRIPTION OF RELATED ART

It is known that a column packing composed of silica gel having apolysaccharide derivative supported thereon is useful as a separatingagent for optical isomers of a racemic modification (Y. Okamoto, M.Kawashima and K. Hatada, J. Am. Chem. Soc., 106, p.5357, 1984). However,such a separating agent is poor in solvent resistance since it comprisessilica gel having a polysaccharide derivative which is supported on thesilica gel simply by coating alone. When the separating agent is used asa column packing for liquid chromatography, therefore, some eluentscannot be used.

Accordingly, a separating agent which is composed of a support having apolysaccharide derivative supported thereon and has an excellent solventresistance has been required.

SUMMARY OF THE INVENTION

The present inventors have conducted extensive studies on a separatingagent whereby the above-mentioned problems can be solved withoutdeterioration of the excellent characteristics of a polysaccharidederivative and, as a result, completed the present invention.

Thus, the present invention provides a separating agent for opticalisomers which is characterized by being composed of a polysaccharidederivative which has been immobilized on a support through crosslinkageof polysaccharide derivative molecules only among themselves on thesupport, a process for producing the separating agent for opticalisomers of the present invention which is characterized by crosslinkingpolysaccharide derivative molecules only among themselves on a supportwith the use of a polyfunctional crosslinking agent, a use of theseparating agent for optical isomers of the present invention as acolumn packing for chromatography, and a process for separating amixture of optical isomers which comprises separating the mixture ofoptical isomers from each other by using the separating agent foroptical isomers according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the polysaccharide in the present invention may be any of asynthetic polysaccharide, a natural polysaccharide and a modifiednatural polysaccharide without restriction, so long as it is opticallyactive, those having a high regularity in the mode of binding arepreferable. Examples of the polysaccharide include β-1,4-glucan(cellulose), α-1,4-glucan (amylose, amylopectin), α-1,6-glucan(dextran), β-1,6-glucan (bustulan), β-1,3-glucan (e.g., curdlan,schizophyllan, etc.), α-l,3-glucan, β-1,2-glucan (crown gallpolysaccharide), β-1,4-galactan, β-1,4-mannan, α-1,6-mannan,β-1,2-fructan (inulin), β-2,6-fructan (levan), β-1,4-xylan, β-1,3-xylan,β-1,4-chitosan, β-1,4-N-acetylchitosan (chitin), pullulan, agarose andalginic acid. In addition thereto, starches containing amylose and thelike are involved in the category of polysaccharides. Among them, thosewhich can be easily obtained in a highly pure state, for example,cellulose, amylose, β-1,4-chitosan, chitin, β-1,4-mannan, β-1,4-xylan,inulin and curdlan, are preferable and cellulose and amylose arepreferable in particular.

The number-average degree of polymerization (the average number ofpyranose or furanose rings per molecule) of the polysaccharide is 5 orabove, preferably 10 or above. Although the upper limit of thenumber-average degree of polymerization of the polysaccharide is notparticularly defined, it is preferable that the number-average degree ofpolymerization thereof does not exceed 500 from the viewpoint ofworkability.

An example of the polysaccharide derivative to be used in the presentinvention is a compound which is obtained by reacting such apolysaccharide as those cited above with a compound having a functionalgroup capable of reacting with a hydroxyl group of the polysaccharide bya publicly known method and in which some of the hydroxyl groups of thestarting poly-saccharide form ester bonds or urethane bonds.

Examples of the compound having a functional group capable of reactingwith a hydroxyl group include isocyanic acid derivatives, carboxylicacids, esters, acid halides, acid amides, halides, epoxides, aldehydes,alcohols and other compounds having leaving groups. They may be any ofaliphatic compounds, alicyclic compounds, aromatic compounds andheteroaromatic compounds.

Particularly preferable polysaccharide derivatives to be subjected tothe crosslinkage in the present invention are esters or carbamatederivatives of cellulose or amylose having at least 0.1 unreactedhydroxyl group per glucose unit, compounds having at least 0.1 reactive,functional group per glucose unit in the groups introduced intocellulose or amylose so as to convert it into the ester or carbamatederivative thereof, and the like. As examples of the reactive functionalgroup, hydroxyl group, amino group, mercapto group, carboxyl group andvinyl group may be cited.

Examples of the support to be used in the present invention includeporous organic supports and porous inorganic supports having surfacewhich have been inactivated to thereby prevent them from reacting with acrosslinking agent, and porous inorganic supports are preferable.Appropriate porous organic supports include those composed of polymerssuch as polystyrene, polyacrylamide and polyacrylate. Appropriate porousinorganic supports include silica gel, silica, alumina, magnesia, glass,kaolin, titanium oxide, silicates and the like. As a particularlypreferable support, silica gel may be cited. The particle size thereofranges from 1 μm to 10 mm, preferably from 1 to 1,000 μm and still morepreferably from 1 to 300 μm, while the average pore size thereof rangesfrom 10 Å to 100 μm, preferably from 50 to 50,000 Å. The treatment forinactivating the surface of silica gel can be effected by a publiclyknown method.

Examples of the polyfunctional crosslinking agent to be used in thepresent invention in order to crosslink polysaccharide derivativemolecules exclusively among themselves include polyfunctional isocyanatederivatives, acid chloride derivatives of dicarboxylic acids, diepoxyderivatives and divinyl derivatives. These crosslinking agents may beany of aliphatic compounds and aromatic compounds. As the polyfunctionalcrosslinking agent, diisocyanate derivatives are preferable inparticular.

In the present invention, the one composed of a crosslinkedpolysaccharide derivative which is obtained by selectively crosslinkingthe hydroxyl groups at the 6-position of cellulose or amylose with eachother is particularly preferable.

The crosslinking ratio of the polysaccharide derivative preferablyranges from 1 to 20%. The term "crosslinking ratio" as used herein meansthe ratio of the unreacted hydroxyl groups and/or reactive functionalgroups participating in the crosslinkage to all the hydroxyl groups ofthe starting poly-saccharide., supposing that the unreacted hydroxylgroups or reactive functional groups in the polysaccharide derivativereact with the functional groups of the polyfunctional crosslinkingagent at a ratio of 1:1.

To crosslink either the hydroxyl groups in the polysaccharide derivativewith each other, the reactive functional groups therein with each otheror the hydroxyl groups with the reactive functional groups therein, thepolysaccharide derivative must be supported (immobilized) on a supporthaving surfaces which has been previously subjected to an inactivationtreatment. An example of the method for immobilization is coating of thesupport with a solution of the polysaccharide derivative. The amount ofthe polysaccharide derivative to be immobilized on the support rangespreferably from 1 to 100% by weight, still more preferably from 5 to 60%by weight, based on the weight of the support.

Now an example of the process for producing the separating agent of thepresent invention will be described.

Cellulose is reacted with trityl chloride to thereby give6-0-tritylcellulose. The tritylcellulose thus obtained is reacted with acompound which has a functional group capable of reacting with ahydroxyl group by a publicly known method. Thus, the hydroxy groups inthe tritylcellulose form ester bonds or urethane bonds together with thefunctional groups of the compound having the functional group capable ofreacting with a hydroxyl group. The cellulose derivative thus obtainedis treated with an acid such as hydrochloric acid to thereby eliminateits trityl groups. Thus, a cellulose derivative according to the presentinvention is obtained. The obtained cellulose derivative according tothe present invention is then dissolved in a solvent. Silica gel havinga surface which has been inactivated is coated with the obtainedsolution to thereby give a silica gel coated with the cellulosederivative. The cellulose derivative of the cellulose-derivative-coatedsilica gel is reacted with a polyfunctional isocyanate derivative in adry, inert solvent to thereby crosslink the cellulose derivativemolecules among themselves. Thus, the separating agent according to thepresent invention wherein a cellulose derivative is immobilized onsilica gel can be obtained.

The methods for immobilizing a polysaccharide derivative on a support bycrosslinking the polysaccharide derivative molecules only amongthemselves on the support in the present invention include a methodwherein the crosslinkage is effected in the hydroxyl group moietyoriginating in the starting polysaccharide of the polysaccharidederivative and another method wherein the crosslinkage is effected inthe reactive functional group moiety carried by the groups which havebeen introduced into the polysaccharide in the step of the conversion ofthe polysaccharide into its derivative. The former includes the methodsrepresented by the following reaction scheme. ##STR1##

When the crosslinkage is effected at the reactive functional groupmoiety carried by the groups which have been introduced into thepolysaccharide in the step of converting the polysaccharide into itsderivative, a step of introducing a substituent carrying the reactivefunctional group may be added to each of the processes represented bythe above-mentioned reaction scheme. Namely, when the polysaccharide isconverted into the derivative prior to the crosslinkage, a compoundhaving a functional group capable of reacting with a hydroxyl grouptogether with another reactive functional group may be reacted with thepolysaccharide or the polysaccharide derivative wherein specifichydroxyl groups are protected.

In the separating agent of the present invention obtained by such amethod, a crosslinked polysaccharide derivative which is obtained bycrosslinking polysaccharide derivative molecules among themselves withthe use of a polyfunctional crosslinking agent includes a supporttherein to form such a structure that the support would not be releasedfrom the crosslinked polysaccharide derivative.

The separating agent for optical isomers according to the presentinvention is generally used in chromatographies such as gaschromatography, liquid chromatography and thin layer chromatography.Application thereof to liquid chromatography is particularly preferable.Thus, the separating agent for optical isomers according to the presentinvention is used as a column packing in various chromatographies.

Use of the separating agent for optical isomers of the present inventionmakes it possible to separate a mixture of optical isomers from eachother.

The separating agent of the present invention has an excellent solventresistance and, therefore, is most suitable as a separating agent foroptical resolution.

EXAMPLES

The present invention will be hereinafter described in detail withreference to the Examples, though the present invention is not limitedto these Examples only.

EXAMPLE 1 1 Surface inactivation treatment of silica gel

Porous silica gel (Daiso SP-1000) was subjected to aminopropylsilanetreatment (APS treatment) by a publicly known method. In 1,000 ml ofmethylene chloride, 200 g of the APS-silica gel thus obtained wasreacted with 15 ml of 3,5-dimethylphenyl isocyanate at room temperaturefor 1.5 hours. The obtained product was separated by filtration with aglass filter, washed successively with a mixture of methylene chloridewith methanol (2/1), methylene chloride, ethanol, acetone and n-hexane,and dried. Thus, silica gel having a surface which had been subjected toinactivation treatment was obtained.

2 Synthesis of cellulose derivative (6-hydroxy-2,3-bis(3,5-dimethylphenylcarbamate) derivative of cellulose)

Under a nitrogen atmosphere, 4.0 g of tritylcellulose having about 0.9to 1 trityl group per glucose unit was dissolved in dry pyridine. To thesolution thus obtained was added 10 ml of 3,5-dimethylphenyl isocyanate.Under a nitrogen atmosphere, the resulting mixture was stirred at 100°C. for 25 hours under heating. The reaction mixture thus obtained waspoured into 700 ml of methanol. The solid thus precipitated wasseparated by filtration with a glass filter, washed successively withethanol and n-hexane, and dried. Next, this solid was introduced intomethanol containing conc. hydrochloric acid. The mixture thus obtainedwas stirred to thereby eliminate trityl groups from the reactionproduct. The solid was separated by filtration with a glass filter,washed successively with ethanol and n-hexane, and dried. Thus a6-hydroxy-2,3-bis(3,5-dimethylphenylcarbamate) derivative of cellulosewas obtained.

3 Preparation of silica gel supporting a cellulose derivative thereon

1.5 g of the cellulose derivative obtained in the above 2 was dissolvedin tetrahydrofuran. The resulting solution was uniformly poured onto 5.7g of the silica gel obtained in the above 1 and the solvent wasvolatilized to thereby support the cellulose derivative on the silicagel. The product thus obtained was washed successively with methanol,ethanol and n-hexane, and dried. Thus silica gel supporting thecellulose derivative thereon was obtained.

4 Immobilization of cellulose derivative on

silica gel through crosslinkage exclusively

among cellulose derivative molecules

To 6.7 g of the silica gel supporting the cellulose derivative thereonobtained in the above 3 was added 35 ml of toluene which had been driedover metallic sodium (hereinafter referred to dry toluene). Further, 110mg of diphenylmethane diisocyanate was added thereto. The mixture thusobtained was stirred at 110° C. for 6 hours under heating. After thecompletion of the reaction, the product was separated by filtration witha glass filter, washed successively with tetrahydrofuran, methanol,ethanol and n-hexane, and then dried. Thus, a separating agent composedof the cellulose derivative immobilized on the silica gel was obtained.

5 Modification of unreacted hydroxyl group in cellulose derivativeimmobilized on silica

To the separating agent obtained in the above 4 were added 25 ml of drytoluene and 15 ml of dry pyridine. Further, 0.5 ml of 3,5-dimethylphenylisocyanate was added thereto. The resulting mixture was stirred at 110°C. for 15 hours under heating. After the completion of the reaction, theproduct was separated by filtration with a glass filter, washedsuccessively with tetrahydrofuran, methanol, ethanol and n-hexane, anddried. Thus,the unreacted hydroxyl groups in the cellulose derivativeimmobilized on the silica gel were carbamoylated.

The amount of the cellulose derivative supported on the silica gel wasabout 19% (calculated by supposing that the cellulose derivative, inwhich 2.5 hydroxyl groups, among 3, contained in the glucose unit ofcellulose had been carbamoylated, was supported on the silica gel).

COMPARATIVE EXAMPLE 1 Preparation of separating agent composed of

polysaccharide derivative immobilized on silica gel through crosslinkageof both polysaccharide derivative molecules among themselves andpolysaccharide derivative with silica gel

1.8 g of tritylcellulose having about 0.9 to 1 trityl group per glucoseunit was dissolved in tetrahydrofuran. The solution thus obtained wasuniformly poured onto 6.0 g of aminopropylsilane-treated silica gel(mfd. by Daiso Co., Ltd.). The solvent was volatilized and thus thetritylcellulose was supported on the silica gel. Onto this silica gelwere poured 75 ml of methanol and 0.75 ml of conc. hydrochloric acid.The obtained mixture was allowed to stand at room temperature overnightto thereby eliminate trityl groups from the cellulose. The product wasseparated by filtration and washed with methanol. 75 ml of methanol and0.75 ml of triethylamine were poured thereonto and the resulting mixturewas stirred for 5 minutes. The product was separated by filtration,washed with methanol, and then dried.

Under a nitrogen atmosphere, a mixture obtained by dissolving 49.3 mg of4,4'-diphenylmethane diisoeyanate in 6.5 ml of dry toluene was added to3.4 g of the silica gel having cellulose adsorbed thereon as obtainedabove. Further, 2.5 ml of dry pyridine was added thereto. The mixturethus obtained was stirred at 60° C. under heating. After 5 hours, 20 mlof dry pyridine and 0.75 ml of 3,5-dimethylphenyl isoeyanate were addedthereto, followed by heating to 110° C. After 18 hours, the reactionmixture thus obtained was filtered through a glass filter and theprecipitate thus obtained was washed with tetrahydrofuran. Theprecipitate was washed successively with methanol, ethanol and n-hexanebefore drying, and then dried. Thus was obtained a separating agentcomposed of the polysaccharide derivative immobilized on the silica gelthrough crosslinkage of both of the polysaccharide derivative moleculesamong themselves and the polysaccharide derivative with the silica gel.

The amount of the cellulose derivative supported on the silica gel wasabout 18% (calculated by supposing that the cellulose derivative, inwhich 2.5 hydroxyl groups, among 3, contained in the glucose unit ofcellulose had been carbamoylated, was supported on the silica gel).

COMPARATIVE EXAMPLE 2 (Preparation of separating agent composed ofsilica gel coated with cellulose tris(3,5-dimethylphenyl-carbamate))

Under a nitrogen atmosphere, 3.5 kg of cellulose (degree ofpolymerization about 300) was added to 56 1 of pyridine. Then,3,5-dimethylphenyl isocyanate was added thereto in large excess (23.1kg) of the cellulose at 100° C. The mixture thus obtained was stirred at105° C. and reacted for 12 hours. Next, the reaction liquid was cooledand 3 1 of methanol was added thereto. The obtained mixture was pouredinto 160 l of methanol. The precipitate thus formed was recovered byfiltration and then dried. Thus, 11.8 kg of cellulosetris(3,5-dimethylphenylcarbamate) was obtained (yield 88%).

720 g of the cellulose tris(3,5-dimethylphenyl-carbamate) thus obtainedwas dissolved in 4.7 1 of acetone. The resulting solution was droppedinto 2,880 g of 3-aminopropylsilane-treated silica gel (Daiso SP-1000)under stirring. The mixture thus obtained was completely mixed and thenthe solvent was volatilized. Thus,3,580 g of a separating agent wasobtained.

APPLICATION EXAMPLE 1

The separating agent composed of a polysaccharide derivative immobilizedon silica gel prepared in Example 1 was employed as a column packing. Itwas packed in a stainless steel column having a height 25 cm in heightand an inner diameter of 0.46 cm by the slurry packing method to therebyprepare a column for optical resolution.

This column was used as such or after washing with various organicsolvents. The optical resolution of various racemic modifications asshown in Table 1 was effected. As the high performance liquidchromatography (HPLC) column, JASCO 875-UV, mfd. by Nippon Bunko, wasused. The experiment was conducted at a flow rate of the eluent of 1.0ml/min and at a temperature of 25° C.

Table 1 shows the results.

The terms given in the table are each defined as follows. ##EQU1##

APPLICATION EXAMPLE 2

The separating agent prepared in Comparative Example 1 was used as acolumn packing and packed into a stainless column having a height of 10cm and an inner diameter of 0.46 cm by the slurry packing method tothereby prepare a column.

After the column thus obtained was washed with various organic solvents,the optical resolution of various racemic modifications as shown inTable 1 was effected with the use of the column. As the high performanceliquid chromatography (HPLC) column, JASCO 875-UV, mfd. by Nippon Bunko,was used. The experiment was conducted at a flow rate of the eluent of0.4 ml/min and at a temperature of 25° C.

Table 1 shows the results.

                                      TABLE 1                                     __________________________________________________________________________                       Column of Ex. 1                                                               just after                                                                             Column of Ex. 1                                                                        Column of Comp. Ex. 1                                       preparation.sup.1)                                                                     after washing.sup.2)                                                                   after washing.sup.3)                     Racemic compd.     k.sub.1 '                                                                        α                                                                          Rs k.sub.1 '                                                                        α                                                                          Rs k.sub.1 '                                                                         α                                                                           Rs                               __________________________________________________________________________     ##STR2##          1.40                                                                             2.19                                                                             7.83                                                                             1.31                                                                             2.06                                                                             6.86                                                                             1.99                                                                              1.55                                                                              2.85                              ##STR3##          1.01                                                                             1. 15                                                                            1.27                                                                             0.99                                                                             1.13                                                                             1.14                                                                             1.37                                                                              not resolved                          ##STR4##          0.81                                                                             1.25                                                                             1.90                                                                             0.81                                                                             1.25                                                                             1.87                                                                             1.00                                                                              1.14                                                                              0.71                              ##STR5##          1.84                                                                             1.17                                                                             1.73                                                                             1.82                                                                             1.16                                                                             1.63                                                                             2.57                                                                              not resolved                          ##STR6##          0.60                                                                             1.53                                                                             2.85                                                                             0.57                                                                             1.61                                                                             3.21                                                                             1.06                                                                              1.30                                                                              1.29                             __________________________________________________________________________     Note)                                                                         .sup.1) The column prepared in Example 1 Eluent: hexane/isopropanol = 9/1     (v/v)                                                                         .sup.2) The one obtained by washing the column prepared in Example 1 with     THF, acetone and methanol at a flow rate of 1.0 ml/min for 30 minutes eac     Eluent: hexane/isopropanol = 9/1 (v/v)                                        .sup.3) The one obtained by washing the column prepared in Comparative        Example 1 with THF and acetone each at a flow rate of 1.0 ml/min for 30       minutes Eluent: hexane/isopropanol = 9/1 (v/v)                           

APPLICATION EXAMPLE 3

The separating agent prepared in Comparative Example 2 was used as acolumn packing and packed into stainless columns each having a height of25 cm and an inner diameter of 0.46 cm by the slurry packing method tothereby prepare 2 columns for optical resolution.

One column as such was subjected to the experiment for opticalresolution of various racemic modifications as shown in Table 2 andthus, the results as given in Table 2 were obtained. The experiment wasconducted under conditions that the eluent was a mixture of hexane withisopropanol (9/1 (v/v)), the flow rate of the eluent was 1.0 ml/min andthe temperature was 25° C.

Another column was washed successively with 4 mixtures ofhexane/isopropanol/tetrahydrofuran (mixing ratio (volume ratio)=9/1/1,9/1/2, 9/1/4 and 9/1/8) and methanol for 30 minutes for and thensubjected to the experiment for optical resolution of various racemicmodifications as shown in Table 2. Thus, the results as given in Table 2were obtained. The experiment was conducted under conditions that theeluent was a mixture of hexane with isopropanol (9/1 (v/v)), the flowrate of the eluent was 1.0 ml/min and the temperature was 25° C.

                                      TABLE 2                                     __________________________________________________________________________                    Column of Comp. Ex. 2                                                                     Column of Comp. Ex. 2                                             before washing                                                                            after washing                                     Racemic compd.  k.sub.1 '                                                                         α                                                                           Rs  k.sub.1 '                                                                         α                                                                           Rs                                        __________________________________________________________________________     ##STR7##       1.75                                                                              3.55                                                                              13.01                                                                             1.09                                                                              3.04                                                                              2.93                                       ##STR8##       1.38                                                                              1.48                                                                              3.62                                                                              0.79                                                                              1.40                                                                              1.03                                       ##STR9##       1.20                                                                              1.13                                                                              1.08                                                                              0.78                                                                              not resolved                                   ##STR10##      2.28                                                                              1.65                                                                              6.36                                                                              1.34                                                                              1.57                                                                              1.62                                      __________________________________________________________________________

We claim:
 1. A separating agent for optical isomers comprising apolysaccharide derivative immobilized on a support, the molecules of thepolysaccharide derivative being solely crosslinked with each otherthrough a crosslinking reaction and at least the surface of the supportbeing inactive to said crosslinking reaction.
 2. The separating agentfor optical isomers as set forth in claim 1 wherein the support is asurface-inactivated silica gel having a particle size of from 1 μm to 10mm and a pore size of from 10 to 100 μm.
 3. The separating agent foroptical isomers as set forth in claim 1 wherein the polysaccharidederivative before the crosslinkage is an ester or a carbamate derivativeof cellulose or amylose having at least 0.1 unreacted hydroxyl group perglucose unit.
 4. The separating agent for optical isomers as set forthin claim 1 wherein the polysaccharide derivative before the crosslinkageis an ester or a carbamate derivative of cellulose or amylose having atleast 0.1 reactive functional group per glucose unit introduced into thecellulose or the amylose so as to convert it into the ester or carbamatederivative thereof.
 5. The separating agent for optical isomers as setforth in claim 1 which is used in chromatography.
 6. The separatingagent for optical isomers as set forth in claim 1, wherein the supportis made of an inert material.
 7. The separating agent for opticalisomers as set forth in claim 1, wherein the polysaccharide derivativehas a crosslinking ratio of from 1 to 20%.
 8. A process for producing aseparating agent for optical isomers comprising the steps of providing apolysaccharide derivative on a support and crosslinking the molecules ofthe polysaccharide derivative solely with each other through acrosslinking reaction in the presence of a polyfunctional crosslinkingagent to immobilize the polysaccharide derivative on the support, saidsupport having at least its surface inactive to the crosslinkingreaction.
 9. The process for producing a separating agent for opticalisomers as set forth in claim 8, wherein the support is made of an inertmaterial.
 10. The process for producing a separating agent for opticalisomers as set forth in claim 8, wherein the support is a silica gel.11. The process for producing a separating agent for optical isomers asset forth in claim 8, wherein the polysaccharide derivative has acrosslinking ratio of from 1 to 20%.
 12. The process for producing aseparating agent for optical isomers as set forth in claim 8 wherein thepolysaccharide derivative before the crosslinkage is an ester or acarbamate derivative of cellulose or amylose having at least 0.1unreacted hydroxyl group per glucose unit.
 13. The process for producinga separating agent for optical isomers as set forth in claim 5 whereinthe polysaccharide derivative before the crosslinkage is an ester or acarbamate derivative of cellulose or amylose having at least 0.1reactive functional group per glucose unit introduced into the celluloseor the amylose so as to convert it into the ester or carbamatederivative thereof.
 14. The process for producing a separating agent foroptical isomers as set forth in claim 8 wherein said polyfunctionalcrosslinking agent is a diisocyanate derivative, an acid chloridederivative of a dicarboxylic acid, a diepoxy derivative or a divinylderivative.
 15. The process for producing a separating agent for opticalisomers as set forth in claim 8 wherein the polysaccharide is celluloseor amylose and the hydroxyl groups at the 6-position of cellulose oramylose are selectively crosslinked with each other.
 16. A process forseparating a mixture of optical isomers comprising the step ofcontacting the mixture with a separating agent comprising apolysaccharide derivative immobilized on a support, the molecules of thepolysaccharide derivative being solely crosslinked with each otherthrough a crosslinking reaction and at least the surface of the supportbeing inactive to said crosslinking reaction, to separate the mixture ofoptical isomers from each other.
 17. The process for separating amixture of optical isomers according to claim 16, wherein the support ismade of an inert material.
 18. The process for separating a mixture ofoptical isomers according to claim 16, wherein the support is a silicagel.
 19. The process for separating a mixture of optical isomersaccording to claim 16, wherein the polysaccharide derivative has acrosslinking ratio of from 1 to 20%.